The Des Moines Register, which is widely considered one of very best indicators of how the results of the Iowa caucuses will turn out, has released their final Republican primary poll. The race is still up for grabs, with Mitt Romney clinging to a narrow lead over Ron Paul. Yet, the most compelling storyline of this last weekend before the primary continues to be Rick Santorum, who has gone “all in” in Iowa and surged in the poll. He needs a great result Tuesday to jump-start a campaign that has yet to catch on nationally.

The poll, conducted Tuesday through Friday, shows support at 24 percent for Romney, the former governor of Massachusetts; 22 percent for Paul, a Texas congressman; and 15 percent for the surging Rick Santorum, a former U.S. senator from Pennsylvania.

But the four-day results don’t reflect just how quickly momentum is shifting in a race that has remained highly fluid for months. If the final two days of polling are considered separately, Santorum rises to second place, with 21 percent, pushing Paul to third, at 18 percent. Romney remains the same, at 24 percent.

“Momentum’s name is Rick Santorum,” said the Register’s pollster, J. Ann Selzer.

Another sign of the race’s volatility: 41 percent of likely caucusgoers say they could still be persuaded to change their minds.

Selzer & Co. of Des Moines conducted the poll of 602 likely Republican caucusgoers, which has a margin of error of plus or minus 4 percentage points. In the final two days of polling, 302 likely caucusgoers were interviewed, with a margin of error of plus or minus 5.6 percentage points.